Rumer Willis Accused of Blocking Ex's Time With Their Daughter

Rumer Willis' ex Derek Richard Thomas is firing back in their custody war ... accusing her of trying to interfere with his time with their daughter.

In new court docs, obtained by TMZ, Derek says Rumer's claims about his alleged drug use, endangering their 3-year-old daughter, Louetta, and refusing to cooperate are "materially false and misleading."

Derek claims it's actually Rumer who has been making things difficult ... saying she repeatedly frustrates his visitation time and fails to follow custody orders.

As TMZ previously reported ... Rumer was awarded primary physical custody of Louetta in June, while she and Derek share joint legal custody. Derek's parenting time was set to begin with monitored visits before eventually moving to unmonitored overnights.

Now, Derek says he just wants that plan left alone and followed.

He's asking the judge to keep the June orders in place -- including his scheduled overnight visits -- while also barring Rumer from taking Louetta out of California or enrolling her in school without his consent.

Derek also claims Rumer treats his supervised visits like a bargaining chip ... pointing to exchanges where he says she offered to loosen monitoring if he agreed to changes elsewhere in their visitation schedule.

And things apparently got heated during a July visit ... when Derek says Rumer showed up with LAPD officers.

According to Derek, cops told them the dispute was a civil matter -- and one officer allegedly pointed out the court order did not say just any nanny could take Louetta from him.

Derek insists he's never flat-out refused supervision ... and says Rumer's emergency attempt to change the custody arrangement should be denied.